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Exchange 2010 Internal Wireless emails received but not sent

Users with mobile devices connected to our internal wireless network are able to receive emial on their device. However, they are unable to send. The sent items just hang in limbo on the devices until they are no longer associated with our wireless network and then they are sent.

The devices are configured to the external mail record: and any incoming mail is routed to IP address
XXX.XXX.XXX.23 which is our exchange server

The server is:
and has an internal IP Address of XXX.XXX.XXX.23 we have created a pointer in DNS for that points to XXX.XXX.XXX.23.

I don't believe this is a DNS issue as the devices can receive email. Not sure what to check next to try and trouble shoot this issue.

Thanks in advance
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Gareth Gudger
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These are Active Sync devices and we are not currently using split-brain DNS
Check the URLs in Server >> Client Access >> Exchange ActiveSync.

What do you have for the ExternalURL and InternalURL? Or are they the same?
Split Brain DNS was the correct solution. As soon as we set up a Zone in AD for .com addresses the wireless email could send and receive.
Does your certificate contain If not ActiveSync won't be able to connect to it.

3rd party certificate providers just stopped allowing for internal names to be used on certificates so internally you will get certificate errors going forward.

I would recommend making the InternalURL match the ExternalURL. Then you will need to configure split-brain DNS so resolves to the internal IP of

The reason you do this is that most firewalls do not permit an internal connection to go out the firewall, resolve DNS and try to come back into the firewall.

I would actually recommend you do this for all InternalURLs, including OWA, ECP, ActiveSync, Offline Address Book, Autodiscover and EWS.

Although this article is for migrating from Exchange 2003 to 2010, it does cover recommend namespace design for 2010 and how to implement. Scroll to Step 5 - Namespace Design.